This invention relates to a dot printer of the type in which received printing data are converted into dot patterns to be printed.
A printer of this type generally includes a main memory which stores data to be printed. Data is read from the main memory and an operation known as "dot-expansion" is carried out on the data. The data resulting from dot-expansion is then stored in a buffer.
A conventional dot printer successively performs the following operations: (1) reading data from the buffer and driving the printing head to print out several lines; (2) reading data corresponding to several lines from the main memory and performing the dot-expansion on that data; and (3) storing the dot-expanded data in the buffer. Thus, the conventional printer applies a full dot-expansion to the printing data every several lines.
The conventional printer is not efficient because it performs substantially the same operations for each page of the document. For example, there are many documents in which all pages are equivalent in content, except for a few isolated parts. Because each page must be entirely subjected to dot-expansion every several lines, the printer must perform substantially the same operations for each page of the document, thus wasting time.